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Combining compost and biochar facilitates moisture improvements and plant growth under field conditions
(2026-03-01)
Kamchoom, Viroon
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Chaisarn, Sumetha
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Ni, Junjun
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Chen, Zhongkui
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Sinsamutpadung, Natdanai
Aims: Using vegetation on degraded soils often faces difficulties due to poor nutrients and limited water retention. Soil amendments such as compost and biochar are therefore required. However, their combined effects on soil and plant development are complex, as intense rainfall and high temperatures in tropical conditions may accelerate amendment degradation and alter soil properties over time. Methods: A two-year field experiment was conducted to monitor soil moisture dynamics, microstructure, vetiver grass (Chrysopogon zizanioides) growth, including shoot height, root depth, and root biomass. Four treatments were compared: unamended soil (S), soil + compost (C), soil + compost + raw biochar (C + RB), and soil + compost + pre-treated biochar (C + PB). Results: S and C treatments exhibited relatively low water retention, associated with smaller proportions of sub-micropores and super-nanopores. C contained more large pores, promoting drainage but causing greater moisture fluctuations. In contrast, C + RB enhanced water retention by increasing fine-pore volumes, while C + PB achieved the highest and most stable soil water content. The improved moisture conditions in C + PB corresponded with deeper rooting and greater root biomass compared with other treatments. Conclusion: Pure compost promoted early plant growth but was less effective over multiple wet–dry seasons, as its organic matter decomposed rapidly under tropical conditions. Combining compost and biochar, particularly pre-treated biochar, offers a practical, field-ready approach to improve soil structure and moisture retention, thereby supporting sustained plant growth in degraded soils.
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Biochar Amendment as a Mitigation Against Freezing–Thawing Effects on Soil Hydraulic Properties
(2025-01-01)
Chen, Zhongkui
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Intraravimonmata, Chitipat
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Kamchoom, Viroon
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Chen, Rui
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Sinsamutpadung, Natdanai
Seasonal freeze–thaw cycles compromise soil structure, thereby increasing hydraulic conductivity but diminishing water retention capacity—both of which are essential for sustaining crop health and nutrient retention in agricultural soils. Prior research has suggested that biochar may alleviate these detrimental effects; however; further investigation into its influence on soil hydraulic properties through freeze–thaw cycles is essential. This study explores the impact of freeze–thaw cycles on the soil water retention and hydraulic conductivity and evaluates the potential of peanut shell biochar to mitigate these effects. Peanut shell biochar was used, and its effects on soil water retention and unsaturated hydraulic conductivity were evaluated through evaporation tests. The findings indicate that freeze–thaw cycles predominantly affect clay’s ability to retain water and control hydraulic conductivity by generating macropores and fissures; with a notable increase in conductivity at high matric potentials. The impact lessens as matric potential decreases below −30 kPa, resulting in smaller differences in conductivity. Introducing biochar helps mitigate these effects by converting large pores into smaller micro- or meso-pores, effectively increasing water retention, especially at higher content of biochar. While biochar’s impact is more pronounced at higher matric potentials, it also significantly reduces conductivity at lower potentials. The total porosity of the soil increased under low biochar application rates (0% and 1%) but declined at higher application rates (2% and 3%) as the number of freeze–thaw cycles increased. Furthermore, the characteristics of soil deformation during freeze–thaw cycles shifted from frost heaving to thaw settlement with increasing biochar application rates. Notably, an optimal biochar application rate was observed to mitigate soil deformation induced by freeze–thaw processes. These findings contribute to the scientific understanding necessary for the development and management of sustainable agricultural soil systems.
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The impact of biochar amendment on soil water infiltration and evaporation under climate change scenarios
(2024-10-01)
Apriyono, Arwan
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Yuliana, Yuliana
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Chen, Zhongkui
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Keawsawasvong, Suraparb
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Kamchoom‬, Viroon
Biochar is an eco-friendly material that is potentially used in earthworks to prevent stability and serviceability problems under extreme scenarios. This study aims to examine the effects of biochar amended on water infiltration and evaporation under extreme climate. A series of numerical analyzes were conducted to observe the response of pore water pressure (PWP) to extreme climate variation with an application of biochar composition. Moreover, an analysis of variance (ANOVA) has been performed to investigate the effect of biochar on soil water holding capacity at a low suction range. According to the result, biochar amended can maintain the fluctuation of PWP due to wetting and drying processes under extreme climate scenarios. This is due to the fact that the finer particles of biochar may clog large soil pores, reducing the water infiltration rate. Moreover, the addition of biochar can increase water retention capacity at low matric suction ranges, which can prevent flooding during extreme wet conditions. Further to this, the addition of biochar to the soil can maintain PWP fluctuation at the near surface area under extreme climate, preventing soil desiccation cracks.
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Influence of biochar on the water permeability of compacted clay subjected to freezing–thawing cycles
(2024-06-01)
Chen, Zhongkui
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Kamchoom, Viroon
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Leung, Anthony Kwan
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Xue, Jiaxiang
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Chen, Rui
Seasonal variation of soil surface temperature, such as freezing and thawing, can induce increases in the water permeability in clay by mobilizing clay pore structure. This kind of weather-induced change in clay behavior may worsen the water-sealing performance during the construction and after closure operation of engineered structures such as soil barriers for tailings or man-made slopes. There is limited knowledge towards the influence of freezing–thawing cycles on clay microstructure and saturated permeability (K<inf>sat</inf>). This study investigated the saturated permeability of clay under freezing–thawing cycles and explored the uses of biochar as eco-friendly amendment to manipulate the permeability of compacted clay. Clay specimens were compacted with different initial water contents (30%, 34%, and 38%). The biochar application rates of 0%, 2%, 4%, 8% (by dry weight) were applied to measure their effects on the permeability of clay specimens. Saturated permeability was measured by the falling head tests. Any variation of biochar amended clay microstructure after freezing–thawing cycles was captured by the scanning electron microscope. The K<inf>sat</inf> was reduced by about one order of magnitude when the biochar application rate was larger than 4%. This may be attributed to the increase in the filling of the biochar particles in the clay intra-aggregate pores upon the transport of liquid water during the repeated freezing–thawing processes. The biochar may thus be recommended to minimize the K<inf>sat</inf> of geo-environmental structures in cold regions when sufficiently large application rate was used to facilitate the pore-filling process.
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Investigating the Impacts of Biochar Amendment and Soil Compaction on Unsaturated Hydraulic Properties of Silty Sand
(2023-07-01)
Chen, Zhongkui
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Kamchoom, Viroon
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Chen, Rui
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Prasittisopin, Lapyote
The application of biochar as an environmentally friendly additive for agricultural soils has recently gained significant attention. However, the influence of biochar addition on unsaturated hydraulic behavior at high suction ranges (i.e., exceeding 100 kPa) remains largely understudied. This study investigates the impact of biochar addition on the unsaturated hydraulic properties of biochar amended soil (BAS). The effects of biochar content, particle size, and soil compaction on the unsaturated hydraulic properties of BAS were also considered. Peanut shell biochar was utilized in this investigation and was amended into a compacted silty sand with distinct particle size groups. Soil water retention curves and unsaturated permeability were measured through a series of evaporation tests. Results demonstrate that the impact of soil compaction on the unsaturated hydraulic properties of BAS diminishes at high suction range, regardless of biochar particle size and content. A high degree of compaction reduces the saturated permeability of BAS by minimising soil macropores. On the other hand, incorporating high biochar contents with fine particles into the soil enhances the reduction of unsaturated permeability and the improvement of water holding capacity, thereby making biochar an effective application in soil for sustainability of the agroecological environment.
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Laboratory study of water infiltration and evaporation in biochar-amended landfill covers under extreme climate
(2022-11-01)
Chen, Zhongkui
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Kamchoom, Viroon
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Apriyono, Arwan
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Chen, Rui
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Chen, Chaowei
Biochar has been used as an environment-friendly enhancer to improve the soil hydraulic properties. Previous studies focused on the effect of biochar addition for irrigation in agricultural soils. However, the understanding of the influence of biochar addition on water infiltration in compacted soils as used in landfill covers is limited. This study investigated the effects of peanut shell biochar addition on soil water infiltration with consideration of soil microstructure variations. The performance of biochar-amended soil was also explored under extreme rainfall and drought conditions. In this experiment, peanut shell biochar with particles finer than 0.25 mm was amended into compacted silty sand. Index soil properties and microstructure were observed. One-dimension (1-D) column tests and corresponding numerical modelling were carried out to investigate the performance of this cover material under different climate scenarios. The results suggested that the application of biochar can increase soil porosity, but a significant number of large pores (i.e., larger than 20 μm) was minimized. With the application of biochar, the soil covers thus become more efficient in preventing infiltration and percolation. This is also crucial to minimize the need for a relatively large thickness of soil cover. With an increase in porosity, the biochar can improve the soil water retention. Under extreme drought, the application of biochar can reduce the very low pore-water pressure (PWP) in soils by more than 50%. From all of these, peanut shell biochar can potentially be an eco-friendly and more sustainable solution for soil covers, even under extreme climate conditions.
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Landfill gas emission through compacted clay considering effects of crack pathway and intensity
(2022-04-15)
Chen, Zhongkui
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Kamchoom, Viroon
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Chen, Rui
Compacted clay barrier plays an important role in reducing landfill gas transport due to its low gas permeability. There is limited understanding of desiccation cracks and to what extent they can cause preferential pathways of landfill gas through compacted clay barriers. This study investigated the intensity and pathway of desiccation cracks as well as its effects on gas emission through compacted clay. The compacted clay with and without scratched compaction interface was subjected to drying to simulate desiccation cracks. The clay was then extruded from large containers into one dimensional columns to allow observation of crack propagation using an X-ray computerized tomography scanner. After that, gas emission rate was measured from each column under different gas pressures (i.e., 1, 5, 10 and 20 kPa). Furthermore, a simplified method is proposed to predict gas emission rate with consideration of intensity and characteristics of cracks. Test results demonstrated that desiccation cracks were initiated mainly at the center of each container (i.e., within 40% of container dimension). Gas emission rate can be increased at least 10 times with the presence of desiccation cracks (i.e., at gas pressure of 5 kPa). As compared to the depth and continuous pathway of cracks which significantly increased gas emission rate, the discontinuous crack pathway can reduce the gas emission rate by up to 3 times. The findings towards crack characteristics and gas emission observed in this study are crucial for safety design and long-term operation of compacted clay barriers in landfill covers.
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Gas permeability and water retention of a repacked silty sand amended with different particle sizes of peanut shell biochar
(2020-09-01)
Chen, Zhongkui
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Chen, Chaowei
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Kamchoom, Viroon
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Chen, Rui
Biochar has been used as an eco-friendly enhancer to alter soil microstructure and improve the mechanical and hydraulic properties of soil. Recent studies observed that variation in biochar particle size can affect its ability to alter soil microstructures. This poses a challenge to select the proper biochar particle size to manipulate soil properties to favor agricultural applications including crop cultivation or engineering design, such as landfill cover. This study experimentally investigated the influence of biochar particle size on soil microstructures and its effects on water retention and gas permeability (k<inf>g</inf>) of a repacked biochar-amended soil (BAS). Peanut shell biochar with four different sizes, ranging from finer than 0.25 to >2 mm, was amended into silty sand. Change in microstructure of BAS was observed using a mercury intrusion porosimeter. Results indicated that the particle size of biochar played a significant role in altering soil microstructures. The addition of smaller biochar particles (i.e., <0.25 mm) decreased soil mesopores and macropores by ∼19%, resulting in greater water retention and reduction of k<inf>g</inf> by ∼31% at ∼0.35 air-filled porosity. However, the mesopores and macropores of soil amended with larger biochar particles (i.e., >2 mm) increased threefold. This resulted in a reduction of water retention at low matric potential (i.e., lower than −3 kPa) and increased k<inf>g</inf> by up to 93% at ∼0.35 air-filled porosity. These findings indicate that application of smaller biochar particles can enhance the water retention ability of the silty sand and reduce soil k<inf>g</inf>, which is beneficial to the water and air management of the biochar-amended soil layers (i.e., as an aeration layer or sealing layer).

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